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Today, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than 1 million visitors each month. The field of early embryology has grown to include the identification of the stem cell as not only critical to organogenesis in the embryo, but equally critical to organ function and repair in the adult human. The identification and understanding of genetic malfunction, inflammatory responses, and the progression in chronic disease, begins with a grounding in primary cellular and systemic functions manifested in the study of the early embryo.

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Home | Pregnancy Timeline | News Alerts | News Archive July 25, 2013


Above: Brain neurons forming

Related articles:
Neuron, 24 July, 2013 Volume 79, Issue 2
Cover Article: Neural stem cells can divide either symmetrically to expand the stem cell pool or asymmetrically to generate neurons. How the balance between symmetric and asymmetric divisions of neural stem cells is regulated during mammalian brain development is poorly understood. In this issue, Xie et al. (pages 254–265) show that horizontal spindle orientation is required during a distinct time window at the onset of neurogenesis to ensure symmetric division and expand the stem cell pool. Misoriented spindle orientation (oblique or vertical) leads to premature neuronal differentiation and depletion of the stem cell pool. The image (generated by Tibor Kulcsar) shows a collage of developing cortical neurons and two mitotic spindles illustrating the fact that oblique spindle orientation creates neurons.

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Neural simulations hint at the origin of brain waves

For almost a century, scientists have been studying brain waves to learn about mental health and the way we think. Yet the way billions of interconnected neurons work together to produce brain waves remains unknown. Now, computer assisted research brings us closer to an answer.

Scientists from EPFL's Blue Brain Project in Switzerland, at the core of the European Human Brain Project, and the Allen Institute for Brain Science in the United States, show in the July 24th edition of the journal Neuron* how a complex computer model is providing a new tool to solve the mystery.

The brain is composed of many different types of neurons, each of which carry electrical signals. Electrodes placed on the head or directly in brain tissue allow scientists to monitor the cumulative effect of this electrical activity, called electroencephalography (EEG) signals. But what is it about the structure and function of each and every neuron, and the way they network together, that give rise to these electrical signals measured in a mammalian brain?

The Blue Brain Project is working to model a complete human brain. For the moment, Blue Brain scientists study rodent brain tissue and characterize different types of neurons to excruciating detail, recording their electrical properties, shapes, sizes, and how they connect.

To answer the question of brain-wave origin, researchers at EPFL's Blue Brain Project and the Allen Institute joined forces with the help of the Blue Brain modeling facilities. Their work is based on a computer model of a neural circuit the likes of which have never been seen before, encompassing an unprecedented amount of detail and simulating 12,000 neurons.

"It is the first time that a model of this complexity has been used to study the underlying properties of brain waves," says EPFL scientist Sean Hill.

In observing their model, the researchers noticed that the electrical activity swirling through the entire system was reminiscent of brain waves measured in rodents. Because the computer model uses an overwhelming amount of physical, chemical and biological data, the supercomputer simulation allows scientists to analyze brain waves at a level of detail simply unattainable with traditional monitoring of live brain tissue.

"We need a computer model because it is impossible to relate the electrical activity of potentially billions of individual neurons and the resulting brain waves at the same time," says Hill. "Through this view, we're able to provide an interpretation, at the single-neuron level, of brain waves that are measured when tissue is actually probed in the lab."

Neurons are somewhat like tiny batteries, needing to be charged in order to fire off an electrical impulse known as a "spike". It is through these "spikes" that neurons communicate with each other to produce thought and perception.

To "recharge" a neuron, charged particles called ions must travel through miniscule ionic channels. These channels are like gates that regulate the flow of electrical current. Ultimately, the accumulation of multiple electrical signals throughout the entire circuit of neurons produces brain waves.

The challenge for scientists in this study was to incorporate into the simulation the thousands of parameters, per neuron, that describe these electrical properties. Once they did that, they saw that the overall electrical activity in their model of 12,000 neurons was akin to observations of brain activity in rodents, hinting at the origin of brain waves.

"Our model is still incomplete, but the electrical signals produced by the computer simulation and what was actually measured in the rat brain have some striking similarities," says Allen Institute scientist Costas Anastassiou.

Hill adds, "For the first time, we show that the complex behavior of ion channels on the branches of the neurons contributes to the shape of brain waves."

There is still much work to be done in order to arrive at a complete simulation. While the model's electrical signals are analogous to in vivo measurements, researchers warn that there are still many open questions as well as room to improve the model. For instance, the simulation is modeled on neurons that control the hind-limb, while in vivo data represent brain waves coming from neurons that have a similar function but control whiskers instead.

"Even so, the computer model we used allowed us to characterize, and more importantly quantify, key features of how neurons produce these signals," says Anastassiou.

The scientists are currently studying similar brain wave phenomena in larger and more realistic neural circuits.

This computer model is drawing cellular biophysics and cognitive neuroscience closer together, in order to achieve the same goal: understanding the brain. But the two disciplines share neither the methods nor the scientific language. By simulating electrical brain activity and relating the behavior of single neurons to brain waves, the researchers aim to bridge this gap, opening the way to better tools for diagnosing mental disorders, and on a deeper level, offering a better understanding of ourselves.

Brain activity generates extracellular voltage fluctuations recorded as local field potentials (LFPs). It is known that the relevant microvariables, the ionic currents across membranes, jointly generate the macrovariables, the extracellular voltage, but neither the detailed biophysical knowledge nor the required computational power have been available to model these processes. We simulated the LFP in a model of the rodent neocortical column composed of >12,000 reconstructed, multicompartmental, and spiking cortical layer 4 and 5 pyramidal neurons and basket cells, including five million dendritic and somatic compartments with voltage- and ion-dependent currents, realistic connectivity, and probabilistic AMPA, NMDA, and GABA synapses. We found that, depending on a number of factors, the LFP reflects local and cross-layer processing. Active currents dominate the generation of LFPs, not synaptic ones. Spike-related currents impact the LFP not only at higher frequencies but below 50 Hz. This work calls for re-evaluating the genesis of LFPs.

Original press release:http://www.eurekalert.org/pub_releases/2013-07/epfd-nsh072213.php